The field of the invention is casters, and the invention relates more particularly to swivel yoke assemblies of the type used on shopping carts.
There are several trends which have made the prior art swivel yoke assemblies less satisfactory. The first is the use of high pressure cleaning compounds which are ever more commonly used to wash shopping carts. Because of the spraying of the carts with detergent solutions under high pressure, the grease which is originally placed in the bearings tends to be removed. The result is a steel-on-steel contact on both sides of each ball bearing without lubrication which causes the swivel to become very hard to turn and very rough. Secondly, larger shopping carts are being made and are often used in warehouse type of retail outlets where the weight which each shopping cart wheel must bear is much greater than it was in the past.
The ball bearing races on shopping cart yokes have been heat treated in the past to increase their hardness so that the races could withstand the wear caused by the heavier loads. Unfortunately, the heat treating is not only expensive, but it also tends to cause warpage of the formed metal which, in turn, causes constant assembly problems because no two pieces of heat treated, formed races are identical. The result is that after extended periods of use and washing, many swivel yokes no longer swivel smoothly and a better swivel yoke design is needed.